Recently, there has been interest in a new type of light emitting device called a vertical cavity surface emitting laser (VCSEL). Conventional VCSELs have several potential advantages, such as a planar construction, emitting light perpendicular to the surface of the die, and the possibility of array fabrication.
Typically, VCSELs include a first distributed Bragg reflector (DBR), also referred to as a mirror stack, formed on top of a substrate by semiconductor manufacturing techniques, an active region formed on top of the first mirror stack, and a second mirror stack formed on top of the active region. The VCSEL is driven by current forced through the active region, typically achieved by providing a first contact on the reverse side of the substrate and a second contact on top of the second mirror stack.
The use of mirror stacks in VCSELs is well established in the art. Typically, mirror stacks are formed of multiple pairs of layers often referred to as mirror pairs. The pairs of layers are formed of a material system generally consisting of two materials having different indices of refraction and being easily lattice matched to the other portions of the VCSEL. For example, a GaAs based VCSEL typically uses an Al.sub.x1 Ga.sub.1-x1 As.backslash.Al.sub.x2 Ga.sub.l-x2 As material system wherein the different refractive index of each layer of a pair is achieved by altering the aluminum content x1 and x2 in the layers, more particularly the aluminum content x1 ranges from 0% to 50% and the aluminum content of x2 ranges from 50% to 100%. In conventional devices, the number of mirror pairs per stack may range from 20-40 pairs to achieve a high percentage of reflectivity, depending on the difference between the refractive indices of the layers. The large number of pairs increases the percentage of reflected light.
In many applications, a certain laser beam mode structure is required to fulfill the needed functions. For example on the one hand, in data storage applications a spatially single mode beam is needed with a certain amount of power. On the other hand, short distance optical interconnect applications based on multimode fibers, require a multimode beam with appropriate divergence to reduce the modal noise, improve coupling efficiency and meet eye safety regulations. Accordingly, there exists a need for controlling the output beam profile, including the intensity and phase distribution, of these laser devices. This is achieved by modifying the output VCSEL DBR mirror, using electron-beam lithography, x-ray lithography or focused ion beam etching technology.
Therefore, it can be readily be seen that a conventional VCSEL that has integrated as a part thereof a means for controlling the output beam profile, including the intensity and phase distribution, is needed. Thus, there is a need for developing a reliable, stable and cost effective vertical cavity surface emitting laser (VCSEL), that includes a means for phase shaping to control the VCSEL output beam characteristics.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art. Accordingly, it is an object of the present invention to provide a new and improved VCSEL with an integrated means for controlling the output beam for use in single mode and multimode VCSEL applications.
Another object of the invention is to provide a reliable VCSEL for multimode optical communications applications and single mode data storage applications.
And another object of the immediate invention is to provide for a VCSEL with an integrated control for output beam intensity and phase distribution that is fabricated utilizing well known lithography and etching techniques.
Yet another object of the invention is to provide for a highly manufacturable VCSEL with an integrated control for output beam intensity and phase distribution.